In recent years, there has been known a vehicular apparatus that is connected to a communication terminal connectable to a public line network and having a hands-free conversation function for carrying out a conversation using a microphone and a speaker, which are provided in a vehicle. In some of such vehicular apparatuses, with a view to inputting a speech sound of a talker appropriately and enhancing the quality of a conversation speech sound, the microphone serving as speech sound input means may be oriented to selectively input a speech sound from a specific orientational direction (directional direction) thereto. In this case, the orientational direction may be set by physically changing the position or orientation of the microphone itself. Also, as disclosed in Patent Documents 1 and 2, a plurality of microphones may be provided, and an orientational direction may be set by subjecting, to a signal process, speech sounds input to the respective microphones.
In setting the orientational direction as described above, it may be impossible to set the orientational direction appropriately because of, for example, the fact that the position of a microphone with respect to a talker differs depending among vehicles, the fact that a predetermined orientational direction is displaced from an appropriate direction due to the positions of seats or the body type of a talker, or the like. Further, even when the orientational direction is appropriately set at first, this orientational direction may become inappropriate under certain running conditions. Thus, it is conceivable to enhance the quality of a conversation speech sound by adopting the methods of the aforementioned Patent Documents 1 and 2 or the like, specifying the position of the talker, and making a changeover in speech sound as needed.
However, in the case of a hands-free conversation, a transmitted speech sound that is transmitted to a party on the other end of the line is transmitted to a destination of conversation after being subjected to successive signal processes. On the other hand, the process of specifying an optimal orientational direction is executed as a process different from the signal processes of the transmitted speech sound during transmission. That is, a changeover in speech sound means a changeover from a speech sound being subjected to a signal process to a speech sound being subjected to another signal process. If a changeover in speech sound is made under such circumstances, defects such as the instantaneous or intermittent interruption of a transmitted speech sound, the generation of abnormal sound, and the like may be caused. Further, while speech sound recognition is under way, a changeover in speech sound may cause defects such as a decrease in the rate of recognition and the like.
[Patent Document 1] Japanese Patent Application Publication No. 2003-114699
[Patent Document 2] Japanese Patent Application Publication No. 2007-302155